Fractures are common in childhood and constitute the major immediate threat to bone health in children. The distal forearm is the most common site of fracture in children (1 in 9 children sustain a forearm fracture during childhood and adolescence). Recent attention has focused on increasing bone density in children for the prevention of osteoporosis several decades later. Whether skeletal properties contribute to fracture risk in otherwise healthy children is unknown. The relation between bone mineralization and fracture risk is not clear, as bone mineral content and density increase with age along with the risk of fracture. This study will examine the relation between bone mass and density and geometric properties of bone and risk of forearm fracture in children and adolescents who experience injury. The Specific Aims of this proposal are: (1) to determine whether bone density is related to forearm fracture risk in children and adolescents who experience trauma; (2) to determine which bone mass, density or geometric measurement best discriminates between children who fracture and those who do not fracture. These questions will be addressed with a case-control study of 320 children and adolescents between 5-16 years of age that experience injury and have been evaluated at Children's Hospital Medical Center for suspicion of forearm fracture. Bone mass, density and bone geometry of forearm fracture cases and non-fractured injured controls will be compared. Physical activity patterns and dietary intake will be assessed to allow investigation as to whether and how these factors are related to bone measurements and fracture risk. This project will evaluate the importance of increased bone density and differences in bone geometry for preventing forearm fractures in healthy children who experience injury, and will identify the best bone measurement for predicting forearm fractures and the determinants of this measurement. Identification of the most predictive bone measurement is important so that it can be used as an endpoint in intervention trials designed to increase bone mass and density in children. Understanding the determinants of this measurement will inform strategies to promote healthy bone and decrease fracture risk in childhood.